This invention relates to an IC card which protects against misuse by incorporating a self-identification function into the card itself.
This invention also relates an information storage circuit suitable for use in IC cards or the like employing a solar battery. The information storage circuit can keep the stored information intact even if the voltage of the power supply fluctuates due to its dependence on a solar battery.
An example of an IC (integrated circuit) card is disclosed in Japanese Laid-Open Patent Application No. 1986/5389. The IC card disclosed therein includes a data input means, a data display means, and a power supply means and having built-in self-identification features. In other words, a password or personal identification number (PIN) is input by using a keyboard integrated into the card, and, this input personal identification number is compared with a personal identification number already stored in an internal electrically erasable read only memory (EEPROM) of the card. If the two numbers match, it means that the user of the card is its legitimate owner. Therefore, before making a transaction by using this type of IC card, the user inputs his personal identification number, using the keyboard of the card, and, after entering this personal identification number, the user presses the `MATCH` key on the keyboard of the card to initiate the comparison of the personal identification number just entered with the identification number already stored in the card. If the two numbers match, an `OK` message is displayed on a liquid crystal display of the card for a duration of about 10 seconds, indicating that the user of the card is the legitimate owner of the card. The card can then be used to make the transaction, only within the time interval during which the `OK` message is being displayed. If the two numbers do not match, this `OK` message is not displayed and the card counts up a counter in the EEPROM of the card which contains the number of times this mis-match occurred. Moreover, a message requesting the user to re-input the personal identification number is displayed on the display means of the card.
However, in the type of the identification card described above, since the duration for which the card is usable for making a transaction after inputting the correct personal identification number is as short as 10 seconds, the card is associated with the following problems: (1) The transaction-enabling duration may be over while the user is queuing in front of the counter after the transaction OK is set. In such a case, the personal identification number must be input again. (2) Moreover, the card owner must input his personal identification number in the vicinity of the terminal device such as ATM, and the personal identification number may be divulged to others.
Moreover, where the power supply of the prior art IC cards is a solar battery, as in Japanese Utility Model Application No. 1987/68811, if the card is passed through the dark when inserted into the bank terminal, the power supply voltage drops, and as a result, the above mentioned `OK` message disappears. This problem also occurs whenever the power supply voltage drops as a result of insufficient amount of light for the solar battery, for example when the card is turned over or is kept in a pocket.
The simplest way to solve this problem is to employ an ordinary battery in the IC card instead of the solar battery, and then us a monostable multivibrator circuit to hold the output signal active for a fixed time interval. However, this method is not practicable since interchanging the battery cells in the IC card is a cumbersome process.
For devices like IC cards, the output signal must be held active for a fixed time interval, after which it should be automatically deactivated. Such devices are generally affected by a drop in the power supply voltage.